The invention relates to the field diffractive optics, and in particular to multiple-wavelength binary diffractive lenses.
Diffractive optics sculpt the propagation of light to generate complex intensity and phase patterns downstream. They achieve this by imposing a particular phase and intensity pattern on the incident light. Phase-only diffractive optics, as their name implies, affect only the phase, and hence are lossless. Binary-phase diffractive optics impose only two-levels of phase. This significantly eases the fabrication of such elements. The phase shift is achieved via an optical-path difference between alternate zones. Such optics inherently exhibit chromatic aberrations.
There have been several approaches to design multiple-wavelength diffractive optics. A heterogeneous design, based on materials with differing refractive indices and dispersion to compensate for chromatic aberration, was proposed. By using phase shifts that are integer multiples of 27, harmonic diffractive lenses can be designed for specific discrete wavelengths. However, the selection of the design wavelengths is limited. A nonlinear optimization technique was used to design dual-wavelength diffractive beam-splitters. Blazed higher-order diffractive optics may also be designed for multiple wavelengths. In all these cases, the fabrication of the diffractive optic is difficult, either due to the multiple levels of phase-height or due to large aspect ratios.